Manually add TFM for Microsoft.Fx.Portability
Manually add TFM for Microsoft.Fx.Portability

The assemblies produced by `DNU pack` do not get stamped with the TFM. There is an issue
tracking this on the DNU side at http://github.com/aspnet/dnx/issues/1802

conniey/dotnet-apiport,Microsoft/dotnet-apiport,mjrousos/dotnet-apiport,mjrousos/dotnet-apiport,twsouthwick/dotnet-apiport,twsouthwick/dotnet-apiport,JJVertical/dotnet-apiport,mjrousos/dotnet-apiport-old,JJVertical/dotnet-apiport,Microsoft/dotnet-apiport,conniey/dotnet-apiport,Microsoft/dotnet-apiport,conniey/dotnet-apiport